Implant with attached element and method of making such an implant

ABSTRACT

A tubular implant having an axial end to which is attached a ring of spoons of a material different from that of the implant. In another aspect, the invention provides a method of attaching elements to an axial end of a tubular implant comprising the steps of providing said elements on one end of a support tube having a radius substantially that of the implant in its unexpanded configuration, abutting the implant and elements end-to-end, fixing the elements to the implant; and parting the elements from the support tube. In a third aspect, the invention provides an implant carrying an element of another material, the element and implant having complementary tapered mating surfaces for achieving a taper form fit of the element onto the implant.

FIELD OF THE INVENTION

[0001] This invention relates to an implant, such as a stent formed froma stent material, to which is attached at least one element, such as amarker, made from a different material, such as a material having aradiopacity greater than that of the implant material. The inventionalso relates to a method of making such an implant.

[0002] Although the present invention has particular usefulness forattaching radiopaque markers to stents, it also has application toimplants (filters, for example) other than stents, and to elements otherthan markers. Such elements could function as, for example, drugdelivery vehicles, trauma inhibitors, or connectors to link the implantto another implant or to an implant extraction tool.

BACKGROUND ART

[0003] WO-A-95/03010 discloses a stent in the form of a metal tubehaving a long axis, a luminal surface and an abluminal surface, and atube wall thickness, the tube carrying within the wall thickness aradiopaque marker made of a metal more radiopaque than the metal whichforms the tube.

[0004] The stent of WO 95/03010 is created from a flat sheet ofstainless steel material, by photochemical etching away of selectedareas of the metal sheet, to leave behind an open lattice-work pattern,which is then rolled up into a tubular shape. A small round opening isprovided at each end of the lattice area. Into each of these openings(called “eyelets”) can be pressed a radiopaque marker of material suchas gold, platinum, tungsten or iridium. The markers are positioned inthe eyelets by crimping.

[0005] EP-A-800 800 also addresses the problem of poor radiopacity ofstents, but advocates a different solution. In a nickel titanium shapememory alloy stent, it is proposed to provide, at one end at least ofthe cylinder which defines the stent, at least one detection elementwhich has the shape of a tongue extending substantially in thelongitudinal direction of the stent, this detection element having awidth, in the circumferential direction of the stent cylinder, which isgreater than the characteristic width, in the circumferential directionof the stent, of each of the struts which make up the lattice workpattern of the stent. It is the greater circumferential width of thetongue which renders it more radiopaque than the thinner struts of thelattice of the stent.

[0006] EP-A-847733 Biotronik discloses a stent which is an aperturedcylinder of titanium, to each end of which is welded a meander-form ringof tantalum. The radiopacity of tantalum being much greater than that oftitanium, this construction allows the locations of the ends of thestent cylinder to be determined radioscopically.

[0007] WO-A-00/64375 ACS was published Nov. 2, 2000, that is, after thepresent priority date. It discloses a stent made from wire or tube butwith end rings of a material more radiopaque that its lengthwise centresection. Materials suggested for the centre section comprise Ni—Ti shapememory alloy (Nitinol) and stainless steel. Materials suggested for theend rings comprise tantalum, platinum, gold and platinum-iridium. Toattach the end rings to the centre section, it is suggested to use,inter alia, laser welding.

[0008] EP-A-709 068 Medinol discloses providing stent ends with“protrusions having enough metal therein to make them X-ray visible”.Gold and tantalum are mentioned as materials which are more visibleunder X-ray illumination than the stainless steel metal of the stent.

[0009] The disclosure of U.S. Pat. No. 6,022,374 is similar to that ofWO-A-95/03010 mentioned above, in that it discloses an insert ofradiopaque material within an eyelet formed in the stent. Mentioned asradiopaque materials are gold, platinum and alloys thereof.

[0010] DE-U-29904817 discloses a stent with axially extendingprojections at one end, at least. These projections can exhibit athickening at their outer cantilevered ends. This concept can becompared with the disclosure of EP-A-800800, mentioned above.

[0011] U.S. Pat. No. 5,741,327 Frantzen discloses a stent withradiopaque markers attached to the ends of the body of the stent. In oneembodiment, a circumferentially continuous serpentine marker element isattached to each end of the stent. This marker element can be of gold,silver, platinum or an alloy thereof. It is disclosed that the body ofthe stent can be from a nickel-titanium alloy. The circumferentialmarker is radially expansible along with the body of the stent. Acircumferential marker is attached to an end of the stent body using oneof a number of techniques including brazing, mechanical fastening,weaving or epoxy adhesive. One specific system of attachment disclosedinvolves the use of “receivers” that extend from the ends of the stentbody. These receivers are configured to receive “tabs” provided on themarker ring. Each tab has a neck and a knob at the end of the neck andthe knob is received into a co-operating rounded space of the receiverof the stent body. A laser is used to achieve local melting so that thereceiver and tab are fused together.

[0012] The disclosures of WO 97/33534 is similar to that of WO 95/03010,in that it includes radiopaque rivets set in a atent of less radiopaquematerial.

SUMMARY

[0013] It is one object of the present invention to provide an implant,such as a stent, with an element of different material, securely fixedto the implant as such.

[0014] It is a more particular object of the present invention toprovide a nickel-titanium shape memory alloy stent with a radiopaquemarker which is compatible with the alloy of the stent; and biologicallyacceptable, and which is more effective and reliable than previousproposals.

[0015] According to one aspect of the present invention there isprovided an implant as defined in claim 1 below. In a second aspect,there is provided an implant as claimed in claim 17 and, in a thirdaspect a method of attaching elements to an implant is provided, asclaimed in claim 16.

[0016] With a ring of elements in the form of spoons, attached at oneend of a tubular implant such as a stent, a more or less complete ringof attached material is presented in the radially compact deliverydisposition of the stent, yielding potentially enhanced radiopacity.Even in the expanded disposition of the stent, a relatively small numberof wide area spoons, say four, delivers relatively good radiopacity.However, the radiopacity in the compact disposition is particularlyhigh, so that the present invention opens up the possibility toeliminate the previously indispensable radiopaque marker ring on thestent delivery system which reveals the location of an end of the stent.This in turn opens up the way to make delivery systems which are simplerin construction than the systems used up to now.

[0017] If interfitting shapes of the stent ends and attached elementsare cut by a laser with its line of action always radial to the stentcylinder, then a frusto-conical form fit between the stent and eachattached element is achieved, enhancing the security of attachment andthe precision of placement of each element attached to the stent.

[0018] This frusto-conical form fit is particularly helpful when it issuch that disengagement of the form-fit occurs by a radially-outwardmovement of the element relative to the stent cylinder. This is because,when the stent expands into its installed configuration, there isradially-inward pressure on the attached element from the surroundingbodily tissue, which resists its disengagement from the stent. Thisresistance complements and reinforces whatever other system is employedto fix the element to the stent.

[0019] Systems to fix an element to an implant can include welding,brazing, soldering, glueing, friction welding or variations ofmechanical interlocks and press-fit configurations.

[0020] When creating stent lattices from sheet material, tubular sheetstarting material is often considered advantageous. However, flat sheetmaterial also is advantageous in some systems, such as those in whichthe stent element is rolled up like a carpet. When laser-cutting thelattice, the above-mentioned frusto-conical form fit can be readilyengineered when cutting the sheet in planar form.

[0021] In a particularly advantageous embodiment, a stent is formed fromsheet material in the form of a tube, and is provided at each end with aplurality of marker carrier portions, to each of which is mounted aradiopaque marker of radiopaque material, in the form of a spoon. Eachof the carriers has a luminal surface, an abluminal surface, and aperipheral surface through the thickness of the stent tube. It is thisperipheral surface which provides one of two complementary matingsurfaces for making the stent/marker attachment. The complementarymarker itself has two major surfaces, one of which is luminal and theother is abluminal, and a peripheral surface around the major surfaces.However, within the area of the major surfaces is a cavity portion. Theperiphery of this cavity defines a female element for engagement with amale portion of the stent tube marker carrier portion, the male andfemale peripheral surfaces providing complementary tapering form-fitsurfaces.

[0022] Preferably each such ring of markers has four marker spoons init. Increasing beyond four reduces the size of each marker. In theexpanded configuration of the stent, visibility of the stent increaseswith the physical area of each separate marker, so large markers arepreferred because they make the expanded stent more visible.

[0023] It is preferred that the markers together make a more or lesscontinuous ring around the stent in its small diameter configurationprior to its deployment by expansion.

[0024] According to the second aspect of the present invention there isprovided a method for making from sheet material a tubular implant, suchas a stent, which expands, during its deployment, from a smaller radiusdelivery disposition to a larger radius deployed disposition, the methodcomprising the steps of:

[0025] 1. providing at least one terminal element on one end of asupport of sheet material arranged as a cylinder with its radius beingthat of the said delivery disposition;

[0026] 2. presenting the tubular implant in its smaller radius,end-to-end with the support, such that the terminal element abuts theimplant;

[0027] 3. fixing the terminal element to the implant; and

[0028] 4. parting the terminal element from the support.

[0029] One of the problems involved in fixing radiopaque markers tostents is the difficulty of aligning the markers with the stent in orderto fix the markers to the stent in exactly the right orientation andposition relative to the stent as such. This second aspect of theinvention ameliorates this problem by presenting markers as terminalelements on one end of a cylindrical support of sheet material which hasthe same radius as the stent in its unexpanded disposition. This isbecause it is relatively easy to arrange in co-linear fashion thecylinder of the stent and the cylinder of the support and, with both ofthese items having the same radius, the cylindrical end surface of thesupport would be in abutment with the cylindrical end surface of thestent. Now, if the cylindrical end surface of the support exhibits aplurality of terminal elements which are destined to become elementsattached to the stent, the process of fixing these markers to the stentcan be effected by welding the elements to the end of the stent, whilethey are in end-to-end abutment with the stent end. Then, when thiswelding step has been completed, it should be a simple further step topart the marker elements from the support cylinder, for example, bylaser-cutting through the thickness of the sheet material which formsthe support.

[0030] It will be appreciated that the terminal elements will have thecurvature of the support cylinder, which curvature will correspond tothe curvature of the stent in its delivery disposition. Thus, when thestent expands to its deployed disposition, and the curvature of theterminal elements remains unchanged, these elements will have a radiusof curvature somewhat smaller than the radius of the expanded stentcylinder. However, this discrepancy in curvature will not be significantbecause the terminal elements will be, to a greater or lesser extent,embedded in the bodily tissue forming the wall of the lumen in which thestent is deployed. Indeed, the elements might have no curvature at all.This would be the case if, for example, the main stent manufacturingsteps are performed on flat sheet material, while it is planar, with thestent lattice then being rolled up for installation into a deliverysystem. The rolling up step would impart a curvature to the stent, butnot necessarily to the attached elements.

[0031] The invention is particularly well adapted to the technical fieldof shape memory alloy stents, specifically those made of Nitinol, andthe attachment to them of terminal marker elements of tantalum.

[0032] In order to make Nitinol stents more visible to radiation, by theprovision of tantalum markers, one would wish to import a greater massof tantalum, but without any increase in the wall thickness of the stentat the locations of the markers. The ideal stent has minimal wallthickness, not only for keeping the stented bodily lumen as open tofluid as possible, but also to keep the stent delivery system with assmall a cross-sectional profile as possible. The present inventionfurthers this objective, in the following way.

[0033] The cylinder of sheet material which provides the terminalelements and support tube is amenable to laser-cutting of the terminalelements out of the material of the tube. Accordingly, virtually all ofthe material forming the circumference of the tube is available forcontribution to the making of the terminal elements. The terminalelements can take up the entire circumference of the support tube,except for the thickness of the laser cuts between adjacent terminalelements around the circumference. Accordingly, for the stent in itssmall radius delivery disposition, there could be virtually an entirecircumference of radiopaque tantalum marker material provided at eachend of the stent, with the only breaks in the continuous ring around thecircumference being the laser cuts between adjacent marker elements.

[0034] In one specific embodiment, there is laser-cut from the supporttube a pattern of four terminal marker elements, each extending aroundone quarter of the circumference of the support tube. Each of thesemarker elements takes up virtually ninety degrees of the circumferenceof the stent in its delivery disposition.

[0035] The exact shape of the outline of each terminal element, and theexact shape of the abutment surface on it which contacts thecorresponding abutment surface of the end of the implant, is a matter ofdesign freedom and choice. At the moment, for implants which are stents,and attached elements which are radiopaque markers, it is contemplatedto provide each element with more or less straight sides to face theadjacent marker elements around the circumference of the stent, but withan arcuate end surface and a female rebated internal abutment surface toreceive a corresponding arrowhead shape male marker carrier portion onthe end ring of the stent. Such a pattern of shape features is describedin more detail below by reference to the accompanying drawings.

[0036] With a male/female interfit of the marker element and stent endring carrier portions, with rebated surfaces, and with the respectiveperipheral mating surfaces extending along radial lines to the stentcylinder, a snap fit interengagement of the stent cylinder and supportcylinder can be arranged, further helping to accomplish the objective ofprecise position and orientation of the marker elements relative to thestent cylinder.

[0037] In any event, a convenient way to fix permanently and reliablythe tantalum marker elements to a Nitinol stent cylinder is bylaser-welding. When laser-cutting the lattice of a stent from a cylinderof sheet material, the line of action of the laser is invariably on aradius of the tubular workpiece. If the co-operating surfaces of thestent, and of its spoons, end elements or markers, are both cut with alaser on a radial line of action, then there will tend to be aself-centering and self-aligning effect when the support tube is offeredup, end-to-end to the stent in its small radius of compressedconfiguration. This effect enhances the value of the method of thepresent invention in building stent assemblies to precise tolerances andwith its end elements securely attached.

[0038] For a better understanding of the present invention, and to showmore clearly how the same may be carried into effect, reference will nowbe made, by way of example, to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a view from the side of a stent tube, looking along aline which intersects the long axis of the tube and is perpendicular toit the stent being in its smaller radius delivery configuration; and

[0040]FIG. 2 is the view of FIG. 1, but with the stent in its deployed,relatively large radius disposition;

[0041]FIG. 3 is a micrograph taken on a section through the line III-IIIshown in FIG. 2;

[0042]FIG. 4 is a micrograph taken on a section through the line IV-IVshown in FIG. 2; and

[0043]FIG. 5 shows schematically a stepwise manufacturing process.

DETAILED DESCRIPTION

[0044] Skilled readers will appreciate that the material of the stenttube and its markers lies all in a circular cross-section with a wallthickness as small as possible, so as to be consistent with theobjective of maintaining a bodily lumen as open as possible. The stentcylinder can be formed from seamless tubular starting material, or fromflat material rolled into a tube (which thus exhibits some sort ofseam).

[0045] Skilled readers will also be well aware that there have been avery large number of proposals for strut patterns in the tubularconfigurations of stents. Whereas FIG. 1 shows an expandable strutpattern in a form which is particularly preferred for the presentApplicant, nevertheless any other strut pattern will have points in itwhich define an end to the cylinder of the stent, and therefore willhave points at the ends of the stent cylinder where markers can beattached.

[0046] Readers will also appreciate that self-expanding stents aredelivered to stenting locations in a radially compressed form, so thatthe aggregate length, in the circumferential direction, of all of themarkers in any particular ring around the axis of the stent tube cannotexceed the circumference of the stent tube in its compressed deliveryconfiguration. In the embodiment shown in FIG. 1, each of the fourmarkers has a circumferential length just less than the circumferentiallength of three cycles of the zigzag pattern which defines the end ringof the stent cylinder so that, when the stent cylinder is compressed,with all the struts of the zigzag ring laying close to each other, theadjacent radiopaque markers will also lie closely adjacent each other inthe circumferential direction.

[0047] As can be seen in FIG. 1, the end ring 12 of the stent cylinder10 is constituted by a succession of struts 14 which zigzag their wayaround the full circumference of the ring 12. There is a vertex 16 whereeach two successive struts intersect, with the end of the stent cylinderbeing defined by the succession of vertices 16. A marker carrier portion18 is located at every third end vertex 16, and fitted to each carrierportion 18 is a marker element 20. In the illustrated embodiment, thestent is made from Nitinol, nickel-titanium shape memory alloy, and eachmarker element is of tantalum. In other embodiments, the stent could beof stainless steel. The attached elements could be of tantalum,platinum, gold or iridium, for example.

[0048] Referring now to FIGS. 3 and 4 together, the tantalum marker 20has a luminal surface 22 and an abluminal surface 24, with the abluminalsurface 24 being in line with the abluminal surface 26 of the stentcylinder and the luminal surface 22 of the marker being in line with theluminal surface 28 of the stent cylinder. FIG. 4 shows that theperipheral surface 30 of the carrier portion 18 is frusto-conical, withthe small end of the cone lying radially inside the stent cylinder. Themarker 20 has a co-operating complementary frusto-conical mating surface32, therefore also defining part of a cone with its vertex lyingradially inside the stent cylinder. It will be appreciated thatachievement of the form fit-shown in FIG. 4 is by advancing the carrierportion 18 radially inwardly into the cavity defined by surface 32 ofthe marker 20 until there is a tight fit between the two complementaryfrusto conical surfaces 30 and 32, corresponding with a lining up of theluminal and abluminal surfaces of the stent cylinder and marker.

[0049] In FIG. 4 surfaces 24 and 26 face a bodily lumen wall. The stentcylinder 10 with its end ring 12 and its carrier portions 18 are servingto hold back the bodily lumen wall tissue from radially inwardencroachment (upwards in FIG. 4). The tissue presses radially inwardalso on the marker 20, tending to dislodge the form-fit. However, inlaser-welding the tantalum spoon 20 to the Nitinol carrier portion 18,melting and flow of tantalum around the tantalum spoon achievesre-entrant locking surfaces, as can be seen on the photomicrograph,which effectively resist such dislodging.

[0050] The present invention aims to assist the attachment of tantalummarkers to Nitinol stents, for example by laser-welding, and make iteven more reliable and secure. The melting point of tantalum is around3000° C., and that of Nitinol around 1200° C., rendering it difficult toachieve a good bond purely by welding. However, the frusto-conical closefit between the two metals, and the flow of Nitinol around the tantalumduring welding, achieves a secure mechanical interlock between the stentand the marker 20.

[0051] It is conventional to form the lattice patterns of Nitinol stentsby laser-cutting. The line of action of a laser for cutting thefrusto-conical mating surfaces 30 of the carrier portion 18 in the stentare achieved by aligning the laser in the normal radial direction ofintersecting the long axis of the stent tube.

[0052] As to the number of markers in one circumference of the stent,optimum radiopacity is accomplished when the markers at each end of thestent make up a virtually unbroken solid ring of marker material aroundthe full circumference. In the case shown there is a marker on everythird end vertex of the stent, with 4 markers at each end of the stent,and 12 zigzag vertices around the circumference of the stent. This,however, is not to exclude the possibility of fewer markers at each endof the stent, including the extreme case, seen in wo 95/03010, mentionedat the beginning of this specification, that there is only one marker ateach end of the stent cylinder.

[0053] Turning now to the second aspect of the invention, and to theassembly of the markers 20 onto the stent 10, one can see from FIG. 1how the four markers 20 at each end of the stent cylinder form avirtually unbroken ring of material having a diameter exactly the sameas that of the stent cylinder 10 in the delivery disposition of FIG. 1.Not shown in

[0054]FIG. 5 shows the four adjacent markers 56 are all cut from asingle tube of tantalum material having the same radius as the stentcylinder 10, a laser having been used to cut around the periphery ofeach marker, including the rebated portion in the centre of the markerwhich receives the marker portion 18 of the stent. The only place wherethe thus cut marker element 56 remains attached to the carrier tube isat the central tip 40 (FIG. 1) of the arcuate surface 42 which definesthe peripheral end surface of the marker 20 remote from the stentcylinder 10.

[0055] A support cylinder 54 which includes the four markers 20, 56attached at their tips 40 is offered up to the stent cylinder 10, thetwo cylinders being co-linear and coaxial. There is then a snap fit ofthe marker portions 18 of the stent 10 into the receiving recess of eachmarker 20. Once the marker portions 18 are secure within the recesses ofthe respective markers 20, a laser can be deployed to produce a laserweld between the marker portion 18 and the marker 20. During welding;the Nitinol adjacent the tantalum marker melts locally and to a limitedextent flows around the tantalum, thereby effectively form-locking themarker to the stent. With this laser welding accomplished, a laser canthen be brought into play, to part at marker tip 40 each individualmarker 20 from the carrier tube 54 which has supported it up to thatpoint. With this parting away of the markers 20 from their carrier tube,the stent can then be separated from the carrier tube, with the markers20 securely welded to the stent 10.

[0056] Readers will immediately appreciate from the above description,taken in conjunction with the drawings, that the markers 20 have thegeneral form of a spoon. That is to say, the markers have two majordimensions and one minor dimension, namely, the thickness in the radialdirection of the stent. The two major surfaces have a length directionin the length direction of the stent and are more or less flat in thatdirection. However, in the transverse direction, circumferential withrespect to the stent cylinder, the markers are curved so that theyexhibit a luminal surface which is concave and an abluminal surfacewhich is convex. This curvature is also exhibited in the transversedirection of a cutlery spoon.

[0057] Further, each marker 20 has a near end surface in which issomething akin to the shaft of a cutlery spoon, namely, the markerportion 18 of the stent. Opposite this end surface is another endsurface, relatively remote from the stent, which is not attached to thestent and is arcuate on its periphery. This is reminiscent of thearcuate (in the sense of presenting an outwardly convex shape)peripheral end surface of a cutlery spoon, remote from the shaft of thespoon.

[0058] In FIG. 5 are shown seven steps, in FIGS. 5(1) to 5(7), of aprocess for manufacturing an implant in accordance with the invention,which is a stent of Nitinol having at each of its ends a ring oftantalum spoons.

[0059] Step 1 is to cut with a laser a tube of Nitinol material in orderto produce a stent precursor 50 having at each ends a ring of fourmarker carrier portions 52 each having a shape which has some slightresemblance to an arrowhead shape. In the example shown here, theNitinol tube has a wall thickness of 0.24 mm and a nominal diameter of1.6 mm.

[0060]FIG. 5(2), showing step 2, shows a tube of tantalum 54 which hasthe same 1.6 mm nominal diameter and 0.24 mm wall thickness but ashorter length than the stent precursor 50. At one end of the tantalumtube 54 has been laser-cut a ring of four spoons 56. A narrow bridge ofmaterial 58 at the tip 40 on the arcuate end surface of each spoonconnects each spoon 56 to the tube 54, and a similar narrow bridge 60links each spoon 56 at its widest point to the corresponding point onthe next adjacent spoon 56 on each side. In this way, the spoons are alllinked up in a ring and each individually still part of the tantalumtube 54.

[0061] In FIG. 5(3), step 3 of the manufacturing process includesplacing a core 62 inside the tantalum tube 54, and a surrounding sleeve64 radially outside the tube 54. The core 62 and sleeve 64 do not extendas far as the ring of spoons 56 but terminate just short of that ring.Likewise, Nitinol tube 50 receives a core 66 and a surrounding sleeve 68which again stop just short of the ring of carrier portions 52. In ajig, the two spaced cores 62 and 66 are linked through their outer endsso as to be maintained co-axial and co-linear, which therefore assuresthat the ring of carrier portions 52 and ring of spoons 56 arethemselves co-axial and co-linear. FIG. 5(3) shows each of the carrierportions 52 tilted slightly radially outwardly, to indicate that this isfeasible, for offering up the carrier portions 52 into the correspondingrecesses of the corresponding spoons 56, as explained above, and asshown in FIG. 5(4).

[0062] In FIG. 5(4), it is shown how manual manipulation of the carrierportions 52 can be used to get them into the corresponding recesses ofthe spoons 56, when the cores 62 and 66 are brought closer to each otherin the above-mentioned jig. This manual manipulation, of each individualcarrier portion 52 in turn, is carried out manually, under a microscope.

[0063]FIG. 5(5) shows the carrier portions 52 duly fitted within thecorresponding recesses of the spoons 56.

[0064]FIG. 5(6) differs from the preceding method step of FIG. 5(5) bythe presence of a welding bead 70 which connects each one of the spoons56 with its corresponding carrier portion 52, around the periphery ofthe arrowhead of the carrier portion 52. This welding bead is a resultof a laser-welding step which occurs between illustrated steps 5 and 6but is not shown as such in FIG. 5. In itself, it will be familiar toreaders skilled in Nitinol stent manufacture.

[0065]FIG. 5(7) differs from FIG. 5(6) in that the cores 62 and 66 andthe rings 64 and 68 have been removed, to leave a ring of spoons 56 dulywelded to one end of the Nitinol tube stent precursor 50. With a laser,the bridges 58 and 60 are cut through, so as to release each spoon fromthe tantalum tube 54 and the spoons adjacent to it.

[0066] Clearly, if it desired to place a ring of spoons at the other endof the stent tube 50 then the process can be repeated at this other end.Indeed, in FIG. 5, a ring of carrier portions 72 is shown at the otherend of the stent tube 50.

[0067] Once the spoons have been placed as desired on the precursor tube50 of the stent, then this precursor tube can be subjected to the normalsuccessor manufacturing steps, including the step of expanding the stentprecursor to a desired larger diameter and then annealing it at thatdiameter in order to “set” a stent shape in the austenitic phase of theNitinol material, which is the shape that it is desired the stent shouldrevert to, in the body, upon deployment from a stent delivery system.Such a set shape might include a central cylindrical portion of thestent, and flared portions at each end, with the ring of carrierportions 52 and spoons 56 themselves forming part of the flared portionof the end of the stent. As tantalum has a melting point so much higherthan that of Nitinol, there is no likelihood that the Nitinol annealingstep will in any way adversely affect the spoons and welding beads ateach end of the stent cylinder.

[0068] The scope of protection of the claims which follow is not to belimited to the embodiments described in detail above. Readers willappreciate that the detailed description is to assist in realisingembodiments within the scope of the claim rather than to set a limit onthe scope of protection.

1. A tubular implant having an axial end to which is attached a ring ofspoons of a material different from that of the implant.
 2. An implantas claimed in claim 1 wherein the spoons are of tantalum.
 3. An implantas claimed in claim 1 wherein the implant is of stainless steel.
 4. Animplant as claimed in claim 1 wherein the spoons are laser-welded to theimplant.
 5. An implant as claimed in claim 1 wherein the implant is ofnickel-titanium shape memory alloy.
 6. An implant as claimed in claim 1wherein the spoons engage with the implant with male-femalecomplementary form-fitting portions.
 7. An implant as claimed in claim 6in which each spoon has an axial length between a first end and a secondend, the first end having said form-fitting portion and said second endbeing arcuate in the sense that the second end presents a convex shapeto its environment.
 8. An implant as claimed in claim 1, which is astent which, in use, expands from a delivery configuration to a deployedconfiguration having a diameter larger than that of the deliveryconfiguration.
 9. An implant as claimed in claim 8 wherein each spoonhas luminal major surface and an abluminal major surface, said majorsurfaces being arcuate and within a cylindrical envelope whichcorresponds to the delivery configuration.
 10. An implant as claimed inclaim 9 wherein each spoon extends around slightly less one quarter ofthe circumference of the tube defined by the implant.
 11. An implant asclaimed in claim 10 wherein each of the spoons has parallel straightside edges, with each side edge relatively close to a facing side edgeof the next adjacent spoon, when the implant is in the deliveryconfiguration, and substantially further apart when the implant is inthe deployed configuration.
 12. An implant as claimed in claim 1 whereinthe spoons are radiopaque markers.
 13. An implant as claimed in claim 6wherein the male-female complementary form-fitting portions havecomplementary mating surface portions which lie in a plane whichincludes the long axis of the tube defined by the implant, whereby theform-fitting portions of the spoons and implant respectively have acomplementary tapered form fit.
 14. An implant as claimed in claim 13,wherein the tapered mating surfaces on the spoon constitute the femalepart of the male-female fit.
 15. An implant as claimed in claim 14,wherein each tapered mating surface on the implant has the barbed shapeof an arrowhead.
 16. A method of attaching elements to an axial end of atubular implant comprising the steps of: i. providing said elements onone end of a support tube having a radius substantially that of theimplant in its unexpanded configuration, ii. abutting the implant andelements end-to-end, iii. fixing the elements to the implant; and iv.parting the elements from the support tube.
 17. An implant made of wireor sheet material arranged in the form of a metal tube (10) having along axis, a luminal surface (28) and an abluminal surface (26), and aradial wall thickness between said surfaces, the implant carrying withinthe wall thickness an element (20) made of a material than the materialwhich forms the implant characterised in that: the element and theimplant have complementary tapered mating surfaces (32, 30) forachieving a taper form fit of the element on to the implant.